1. Field of the Invention
The present invention relates to a plasmon generator that couples with light, evanescent light in particular, in a surface plasmon mode and generates near-field light, and a thermally-assisted magnetic head that is provided with the plasmon generator.
2. Description of the Related Art
Currently, along with the advancement of high recording density of a magnetic recording medium (hard disk), further improvement is demanded in the performance of a thin film magnetic head.
A composite type thin film magnetic head that contains a reproducing head having a magnetoresistive effect element (MR element) for reading and a recording head having an inductive transducer for writing is widely used as a thin film magnetic head.
Along with further improvement in the recording density, a new technology is proposed in which a magnetic field for writing is applied to a specified bit of a hard disk to perform magnetic recording while heat is applied to the hard disk to lower a coercive force of the specified bit. Such a technology is referred to as thermally-assisted magnetic recording. Further, a magnetic head for performing the thermally-assisted magnetic recording is referred to as a thermally-assisted magnetic recording head.
In the thermally-assisted magnetic recording, it is preferable that heat is locally applied to a specified recording bit of a hard disk. Therefore, it is conceivable to use near-field light to achieve localized heating.
US 2003/0066944 A1 discloses a near-field light probe (plasmon antenna) that locally generates strong near-field light. The near-field light probe is formed from a metallic scatterer having a shape that is tapered in one direction. The metallic scatterer is directly irradiated with light. The light plasmon-resonates with the metallic scatterer. Thereby, a plasmon is excited in the metallic scatterer.
Due to this localized plasmon, near-field light localized at a front end of the metallic scatterer is generated.
When a front end part of the metallic scatterer is brought close to a recording medium, strong near-field light can be locally applied to a specified bit of the recording medium. This allows a localized region of the recording medium to be efficiently heated.
When the above-described near-field light probe is used, it is known that conversion efficiency for converting the incident light to the near-field light is about 10 to 20%. The remaining 80 to 90% of the light is reflected at a surface of the metallic scatterer or is converted to thermal energy by being absorbed by the metallic scatterer. Usually, the metallic scatterer has a very small volume and may be configured to have a dimension even less than the wavelength of the light. Therefore, due to absorption of energy of the incident light, temperature of the metallic scatterer rises very high. Due to the temperature rising, the metallic scatterer itself may melt.
US 2010/0103553 A1 discloses a plasmon antenna having a configuration different from the above-described plasmon antenna. This plasmon antenna is incorporated into a thin film magnetic recording head. The plasmon antenna has an edge part that couples with light (evanescent light) penetrating from a waveguide in a surface plasmon mode and a front end part that generates near-field light. Specifically, the plasmon antenna is not directly irradiated with light propagating through the waveguide; instead, the evanescent light couples with the edge part in the surface plasmon mode via a buffer layer. A waveguide-type surface plasmon excited by the evanescent light is guided through the plasmon antenna along the edge part. The waveguide-type surface plasmon reaches the front end part of the plasmon antenna and causes near-field light to be generated at the front end part. Due to the near-field light, a specified region (bit) of a hard disk is locally heated.
In the plasmon antenna described in US 2010/0103553 A1, the plasmon antenna is not directly irradiated with an electromagnetic wave; instead, the evanescent light penetrating from the waveguide is used. Therefore, heat generation in the plasmon antenna can be suppressed.
US 2011/058272 A1 also discloses a thermally-assisted magnetic recording head provided with a near-field light generator (plasmon antenna or plasmon generator) that couples with evanescent light in a plasmon mode. In the plasmon antennas described in US 2010/0103553 A1 and US 2011/058272 A1, the waveguide-type surface plasmon is excited.
The plasmon generator described in US 2011/058272 A1 extends long in a direction that intersects with a surface opposing a recording medium, that is, an air bearing surface, and has a substantially V-shape at the air bearing surface. Near-field light is generated at a front end surface of the plasmon generator. However, the near-field light has a spread around not only the V-shaped edge part but also periphery of the edge part. As a result, a recording medium to which the near-field light is applied has a broad heat distribution corresponding to the spread of the near-field light. Due to the broad heat distribution, a bit adjacent to a bit that is originally to be heated may be unintentionally heated so that magnetic information written to the adjacent bit may be unstable. As a result, performance of the magnetic recording may be deteriorated.
Further, in the plasmon antenna that utilizes the waveguide-type surface plasmon, temperature rise during operation is relatively small. However, the small front end part of the plasmon antenna may agglomerate due to heat generation. In particular, when the plasmon antenna is formed of gold (Au), a small portion in a vicinity of a recording-medium-opposing surface (air bearing surface) of the plasmon antenna is likely to agglomerate due to heat. Due to the agglomeration, a shape of the front end part of the plasmon antenna changes and the front end part may be away from the recording medium. As a result, the performance of the magnetic recording may be deteriorated and lifetime of the magnetic head may be reduced.
In order to perform highly reliable magnetic recording, a plasmon antenna (plasmon generator) in which heat generation at a front end part is suppressed and near-field light is locally generated at the front end part is desired.